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Embryology of Urinary System by Dr. Majid Kakakhel
1. EMBRYOLOGY OF URINARY SYSTEM
Nephric System & Its Anomalies
Vesicourethra & Its Anomalies
By:
Dr.MajidJan Kakakhel
PGR-Team C
InstituteofKidneyDiseases, Peshawar.
majidjankakakhel@gmail.com
2. NEPHRIC SYSTEM
• The nephric system develops progressively as
3 distinct entities:
1. Pro-nephros
2. Meso-nephros
3. Meta-nephros
3. Pronephros
• Earliest nephric stage in
Humans.
• Extends from 4th to 14th
somites.
• Conists of 6-10 pairs of
tubules, opens into ducts.
• Disappears completely by 4th
week of embryonic life.
• Rudimentary & non-functional
4. Mesonephros
• Principal excretory organ
during early embryonic
life (4-8weeks)
• Mesonephric tubules
develop from
intermediate mesoderm
caudal to pronephros
shortly before pronephric
degeneration.
5. Mesonephros
• These tubules rapidly
lengthens and form S
shape loop, medial end
forms a cup shape
outgrowth ( Bowmans
capsule) to which tuft of
capillaries is pushed
making glomerulus
• Laterally, other end
connects mesonephric
duct.
6. Metanephros
The Definitive Kidney
• The Final phase of development
of nephric system, originates
from 2 sources:
1. Ureteric Bud
2. Metanephric Mesenchyme
(Blastema)
7. Metanephros
• The ureteric bud grows cephalad and collects
mesoderm from the intermediate mesoderm around
its tip.
• The ureteric bud penetrates the metanephric
mesoderm (blastema)
8. Metanephros
• Here, the bud grows and repeatedly divides.
• The first 3 to 5 generation of branches fuse to form the renal
Pelvis,
• the next divisions become the major calyces,
• while further divisions forms the minor calyces and colleting
tubules.
9. Excretory System
• Each newly formed collecting tubule is
covered at its distal end by a metanephric
tissue cap.
10. • Cells of the tissue cap form small vesicles, the
renal vesicles
12. • One end of the S-shaped tubule becomes cup shape Bowman’s
Capsule , to which capillaries grow, and differentiates into glomeruli.
• These tubules, together with their glomeruli, forms nephrons or
excretory units.
• The other end fuses with the collecting tubules and forms an open
connection, establishing passageway from Bowman’s capsule to the
collecting unit.
13. • Continuous lengthening of the excretory
tubule results in formation of the proximal
convoluted tubule ( PCT), loop of Henle, and
distal convoluted tubule ( DCT).
15. Ectopic Kidney:
• Failure of metanephros
to ascend leads to an
ectopic kidney.
• An ectopic kidney may
be on the proper side
but low (simple ectopy)
or on the opposite side
(crossed ectopy) with or
without fusion.
16. Horse-shoe Kidney:
• Fusion of the paired metanephric masses.
• Lower poles fused in midline in front of L4
• Ascent is impeded by inferior mesenteric
artery
17. Renal Agenesis/ Solitary Kidney:
• When ureteric but fails to contact
Metanephric mesenchyme or when ureteric
bud fails to develop.
18. Duplicated Ureter:
• When An accessory ureteric bud develops
from mesonephric duct, meeting the same
metanephric mass, forms duplicated ureter.
• Rarely, each bud has a separate metanephric
mass, resulting in supernumerary kidneys.
19. URINARY BLADDER & URETHRA
• During the 4th to 7th weeks of development the
cloaca divides into:
1.Urogenital Sinus (Anteriorly)
2.Anal canal (Posteriorly)
20. Urogenital Sinus
Is divided into three
parts;
A cranial; vesical part;
forms most of the
bladder and continuous
with the allantois.
A middle; pelvic part;
forms main part of male
urethra and entire
female urethra.
A caudal; phallic part
grows towards genital
tubercle.
21. Urinary Bladder
It develops mainly from the
vesical part of the urogenital
sinus.
The trigone is derived from the
absorbed caudal ends of the
mesonephric ducts.
The epithelium is endodermal
in origin.
The other layers are derived
from the splanchinic
mesoderm
22. • At first, Urinary bladder
extends upto umbilicus,
where it is connected to the
allantois that extends into
the umbilical cord
• At 15th weeks, the allantois is
obiterated, becomes thick
fibrous cord Urachus
• Urachus extends from apex
of the bladder to the
umbilicus
• In adults it is represented by
median umbilical ligament
23. URETHRA:
The genital tubercle (mesenchymal
elevation) develops at the cranial
end of the cloacal membrane.
Two urethral folds, develop on
either side of the urogenital
membrane.
Laterally two labioscrotal folds
develop on either side of the
urethral folds.
Two urethral folds in male fuse
with each other to close the penile
urethra.
Two urethral folds in female remain
separate to form labia minora.
Labioscrotal folds)
24. The genital tubercle elongates forming the phallus,
which is the precursor of the penis.
Most of the male urethra : prostatic, membranous and
spongy parts is derived from endoderm of the pelvic
part of urogenital sinus.
The distal part of male urethra in glans penis starts as
ectodermal solid cord that grows towards the root of
penis to meet the spongy urethra , later it canalizes.
25. Anomalies:
Urachal anomalies
Extrophy of the bladder
(Ectopiae vesica); exposure
of the posterior wall of the
bladder due to a defect in the
anterior abdominal wall and
anterior wall of the bladder.
26. Urachal anomalies
A, Urachal cyst, persistence
or remnant of epithelial lining
of urachus.
B, Urachal sinus, discharge
serous fluid from the
umbilicus.
C, Urachal fistula, the entire
urachus remains patent and
allows urine to escape from
the umbilicus.
27. Urethral Anomalies
1-Hypospadius : is the
most common anomaly,
with incomplete fusion of
the urethral folds, and
abnormal openings of the
urethra occur along the
ventral (inferior) aspect of
the penis.
2-Epispadius : is a rare
abnormality, in which the
urethral meatus is found on
the dorsum of penis, it is
most often associated with
extrophy of the bladder.
Mesonephros degenerates by 2nd months except few caudal tubules and ducts which makes male genital system
POSITION OF THE KIDNEY • The kidney, initially in the pelvic region,
• later shifts to a more cranial position in the abdomen.
• This ascent of the kidney is caused by diminution of body curvature and by growth of the body in the lumbar and sacral regions.
• In the pelvis the metanephros receives its arterial supply from common iliac arteries.
• During its ascent to the abdominal level, it is vascularized by arteries that originate from the aorta at continuously higher levels.
• The lower vessels usually degenerate, but some may remain
FUNCTION OF THE KIDNEY • The definitive kidney formed from the metanephros becomes functional near the 12th week.
• Urine is passed into the amniotic cavity and mixes with the amniotic fluid.
• The fluid is swallowed by the fetus and recycled through the kidneys.
• During fetal life, the kidneys are not responsible for excretion of waste products,
• The placenta serves this function.
Mesodermal uro-rectal septum
In infants and children the bladder is an abdominal organ , it begins to enter the greater pelvis at about 6 years and becomes a pelvic organ until after puberty.